where \(\bf q\)  is the in-plane wave vector and \(|C_q|^2\)  is the matrix element
of deformation interaction. [1]}
As a result, \((dn/dt)_{ac}\)  is expressed through the two-particle correlation function. Since the main contributions to (6) appears from \(\varepsilon \ne \varepsilon ^{\prime }\) , this correlation function can be decoupled according to
\(\left\langle {\hat{A}_{\varepsilon ^{\prime }} \left( {{\bf x},{\bf x}^{\prime }} \right)\hat{A}_\varepsilon \left( {{\bf x}^{\prime },{\bf x}} \right)} \right\rangle \approx \hat{A}_{\varepsilon ^{\prime },\Delta {\bf x}} \hat{A}_{\varepsilon , - \Delta {\bf x}}\) ,
where \(\hat{A}_{\varepsilon ,\Delta {\bf x}} = \left\langle {\hat{A}_\varepsilon \left( {{\bf x},{\bf x}^{\prime }} \right)} \right\rangle \)  is the
averaged spectral function given by 2\(\times \) 2 matrix.
